1. Field of the Invention
This invention relates to a reflection type photoelectric switch including a light projecting member for projecting a light beam to a retroreflector and a light receiving member for receiving a reflected light beam from the reflector to produce a light path, whereby an object is detected when it blocks the light path, and move particularly to an improved photoelectric switch which can precisely detect even the object having a mirror surface.
2. Description of the Prior Art
A reflection type photoelectric switch housing light projecting and receiving members is well known in which the light projecting member projects a light beam to a retroreflector and the receiving member receives a reflected light beam from the reflector whereby a detection signal is obtained when the projected light beam is blocked by an object to be detected. Such a conventional photoelectric switch, however, has a disadvantage that an object having a metallic or mirror surface cannot be detected thereby because the light beam projected from the projecting member is reflected on the mirror surface to be received by the receiving member.
In order to overcome such a disadvantage, there has been proposed heretofore a photoelectric switch in which a pair of light projecting members respectively project different wavelength lights to a retroreflector and only one of the projected lights is reflected by the reflector so that the discrimination of the reflector and an object to be detected by the switch is performed by the comparison between the levels of the respective reflected lights. This conventional switch needs two pairs of projecting and receiving members, so that the number of optical components is unnecessary increased. Moreover, the respective optical axes of the respective projecting members are slightly shifted, so that a detection signal is erroneously produced when only one of the pair of optical axes is blocked by the object.